The present invention relates generally to restriction indicator devices for automatically detecting and indicating a restriction in filter elements of fluid filters having an intake side and a negative pressure side. More particularly, the present invention relates to a restriction indicator having means for generating an electrical alarm signal in response to an undesirable restriction in the filter element of a fluid filter.
The present invention is an improvement of two prior art restriction indicators. One such prior art restriction indicator is disclosed in U.S. Pat. No. 3,443,365 which is assigned to the assignee of the present invention. This U.S. patent discloses a restriction indicator in which a movable colored signal element is visible through a window portion in the housing of the device when an undesirable restriction occurs. Generally, the subject patent discloses a device having a housing with a transparent wall and which is divided into first and second pressure chambers by a flexible bellows-type diaphragm disposed therein. The first chamber is in fluid communication with the atmosphere while the second chamber is in fluid communication with the negative pressure side of the fluid filter. A spring biases the diaphragm to which the colored signal element is secured to a normal position wherein the colored signal element is not visible through the wall of the housing. Upon increased negative pressure within the second chamber, the bellows diaphragm expands against the spring biasing force such that the colored signal element becomes visible through the housing wall. Means are provided for releasably retaining the diaphragm in the extended or expanded position until the diaphragm may be manually released. The restriction indicator may be mounted on a vehicle instrument panel and communicates with the negative pressure side of the fluid filter through a conduit such as a rubber hose. In such situations, however, consideration must be given to the conduit curvature to reduce air flow resistance and the indicating device should be mounted on a supporting means to cancel the vibration between the vehicle body and the engine. Moreover, connecting means must typically be provided to prevent leakage at the rubber hose connections.
An improved restriction indicator has been disclosed in Japanese utility model Registration No. 90913/75 wherein an electrical signal transmitting means including mechanical make or break contacts are incorporated into the restriction indicator disclosed in the above-mentioned U.S. patent. A visual indicator or alarm means, for example, a display lamp, is mounted on the vehicle instrument panel and connected to the electrical signal transmitting means. The improved restriction indicator includes a switch rod mounted for reciprocating movement in response to the expansion or retraction of a flexible bellows-like diaphragm. A fixed contact is mounted on a fitting for attaching the restriction indicator to an outlet conduit and a movable contact is mounted on the switch rod so that when the switch rod is lowered the contacts are closed whereby the display lamp or arm means is actuated through a suitable electric circuit. In some applications, however, such as large construction machines subject to violent vibration, the mechanical contacts may inadvertently make or break. Thus, an alarm signal may be interrupted or an inaccurate alarm signal generated.
The present invention is an improvement over the two prior art devices discussed above in that it is a restriction indicator providing a reliable and accurate electrical signal utilizing a photointerrupter device. Mechanical contacts are thus eliminated in the present invention thereby insuring that the restriction indicator is substantially unaffected by vehicle or engine vibration.